IdentificationOften described as 'alien-like' in appearance, this gentle giant essentially looks like a huge floating head with fins. It grows up to 4 m long and can weigh almost 5000 pounds (over 2200 kg), making it the world's heaviest bony fish. Instead of a caudal fin (tail) the ocean sunfish has a rudder-like structure called a clavus. It propels itself by flapping its tall dorsal and anal fins from side to side. Instead of scales it has tough elastic brownish-blue to silver skin.

Habitat & RangeThis huge fish is found in tropical and temperate waters around the world. It is an elusive species and so its ecology is relatively unknown, though it appears to spend much of its time near the surface in the open ocean. It is spotted fairly regularly near coastlines of the Pacific Northwest during summer, however, and has even been sighted in protected waters along the BC and Washington coasts. It has been documented as far north as the Gulf of Alaska. Click here to read about an ocean sunfush and killer whale encounter off Calvert Island.

Similar SpeciesTwo other sunfish species exist in the Pacific but appear to be restricted to tropical and subtropical waters.

Intriguing InfoThe ocean sunfish is unusual in many respects. Unlike most bony fish it lacks a swim bladder, ribs, and bony tissue in its skeleton. While a clumsy-looking and usually slow swimmer, it can reach surprisingly good speeds (to 3.2 km/hr) and can even manage to breach the surface of the water while attempting to remove parasites. It will also lie on its side at the surface and drift with the currents; it is thought that this 'basking' behaviour may serve multiple purposes, including thermoregulation and parasite removal, as cleaner fish and even birds will pick parasites off the skin. Up to 40 different genera of parasites use the ocean sunfish as a host, as discussed in the below video.

The ocean sunfish mainly eats jellyfish, such as the sail jellyfish or Velella velella (photo), but will also eat algae, zooplankton, and small fish; it may mistakenly consume plastic bags that resemble jellyfish. It is unable to fully close its small mouth.